1. Field of the Invention
The present invention is concerned in general with acoustics and sound reproduction. In particular, the invention is directed to overcoming some of the interrelated loudspeaker and acoustical problems encountered in the motion picture theater environment.
2. Description of the Prior Art
Substantial advances in motion picture sound quality have been made in the past decade, however a weak link remaining in the cinema sound reproduction chain is the theater loudspeaker system and its acoustic environment.
Very few theaters are currently equipped with loudspeaker systems that incorporate state-of-the-art technology and, indeed, most employ systems using components that were originally designed in the 1940's. Typically, such systems employ horn radiators both in the low frequency and high frequency range, perhaps augmented with sub-woofers for very low frequencies to overcome low bass response deficiencies. Audible distortion at high sound levels with bass program material is common. The mid-range dispersion of such systems is oriented for theaters with balconies (i.e., the best mid-range dispersion is vertical). Multi-cell high frequency horns attempted to produce an output relatively constant in amplitude over a range of output angles and frequencies, yet are substantially inferior to more recent designs. The crossover design and dispersion characteristics lead to a "camel-back" shaped power response that is evident when 1/3-octave pink noise measurements are made in theaters using such systems. The problem is discussed and suggestions for improvement are made in "Cinema Sound Reproduction Systems: Technology Advances and System Design Considerations" by Mark Engebretson and John Eargle, SMPTE Journal, November, 1982, pp. 1046-1057.
Engebretson and Eargle suggest the use of a combination of loudspeaker components that employ many of the state-of-the-art techniques in loudspeaker design, including the use of direct radiators in vented boxes as woofers and the use of so-called "constant directivity" horns having wide dispersion as tweeters. While such a combination presents a useful improvement over the systems commonly in use, the smoothness of the low frequency and high frequency response in such a system is not optimum nor is its sound localization and stereo imaging.